Michigan State University Extension
Preserving Food Safely - 01600598
There are two classifications of pickles, fermented and fresh pack. Fermented pickles (also called brined pickles) are prepared by soaking cucumbers in brine for several weeks. During this period lactic acid bacteria, which are salt tolerant, produce lactic acid from natural sugars in cucumbers. Lactic acid not only preserves the pickles but also imparts a characteristic flavor. Most spoilage microorganisms cannot tolerate the saltiness of the brine and die. Yeasts, which require air, grow as a scum on the surface of brine. This scum of yeasts should be removed daily because they destroy the lactic acid produced by bacterial fermentation and produce enzymes which break down pectic substances in the pickles, making them soft and mushy.
Fresh-pack pickles are prepared by soaking cucumbers in brine for a few hours or overnight, then draining them and covering them with a boiling hot pickling solution containing vinegar and spices. They are not fermented. The vinegar, which should be 5 percent acetic acid, acts as the preservative. The short brining procedure serves two purposes. First, it removes bitter juices present in some cucumbers and enhance the uptake of pickling solution, resulting in a firmer product. Too strong a brine shrivels the cucumbers. Too weak a brine removes too little water, thus making possible undue dilution of the pickling solution with resulting spoilage.
Processing in a boiling-water canner is recommended for both fermented and fresh-pack pickles.